The invention relates to retention of marine propellers, and more particularly to a self-locking propeller nut for retaining a propeller on a shaft and resisting the vibrational forces which ordinarily tend to unscrew a propeller nut.
Various apparatus have been used to retain a screw-on propeller nut on the end of a propeller shaft. Vibration has always been a problem, for it tends to loosen and unscrew almost anything associated with a propeller shaft. A typical scheme, used particularly on inboard-outboard drive systems, has been the provision of a splined area of the shaft, forward of the threaded end, which extends far enough back to extend rearwardly out of the propeller-bearing block. The non-rotational retention of the propeller block on the shaft has of course been the primary reason for the splined shaft. But the short rearward extension of this splined portion provided a mount for a flat annular plate with a correspondingly splined central bore. The outer periphery of this plate had a series of radially extending tabs, which, when the metal propeller nut was screwed in place adjacent to the plate, were bent over toward the nut to engage in a series of depressions in the nut's peripheral edge.
While this system was to some extent successful in preventing vibrational unscrewing of the propeller nut, it was costly in the number of components involved and the extra shaft length for the spline. Moreover, it was time consuming to crimp the multitude of metal tabs onto the propeller nut, and these of course had to be straightened out before the nut could be removed for propeller repair or maintenance. Metal fatigue would prevent the tabbed plate from lasting indefinitely. In service, some rattling could be expected from the strong vibrations acting among the nut, the plate, the shaft and the propeller block.